LONDON (Reuters) - Smog is not just bad for the lungs. It can hit a man's sperm count too, a Californian study revealed on Wednesday.

The University of Southern California looked at the sperm counts of 48 men who donated at least 10 times in two years to a Los Angeles sperm bank.

Using air pollution measurements from the area where each man lived, Rebecca Sokol's team estimated how much pollutant they were exposed to in the days leading up to each donation.

The team, from the University's Keck School of Medicine, found that ozone formed in smoggy air was the only pollutant that appeared to be linked to decreased sperm production. Carbon monoxide seemed to have no effect.

Ozone cannot reach the testicles directly but Sokol, whose findings were published in The New Scientist magazine, said it may cause an inflammatory response or produce toxic substances in the blood that damage sperm.